Photosensitive compositions comprising o-naphthoquinone-diazide compounds and novolak phenol resins have been commercially used for manufacturing lithographic printing plates and as photoresists, as very excellent photosensitive compositions.
However, the novolak phenol resins used mainly as binders have drawbacks to be improved, such as poor contact with substrates, fragile films, inferior wear resistance, or insufficient impression capacity when used for lithographic printing plates, and therefore have a limitation on their application.
To solve such problems, various polymers have been examined as binders. For example, polyhydroxystyrenes or hydroxystyrene copolymers described in JP-B-52-41050 (the term "JP-B" as used herein means an "examined Japanese patent publication") are surely improved in film properties, but still have the disadvantage of inferior wear resistance.
Further, JP-A-51-34711 (the term "JP-A" as used herein means an "unexamined published Japanese patent application" proposes to use polymers containing structure units of acrylic acid derivatives in their molecular structure as binders. However, such polymers have a disadvantage in that a range of conditions for proper development is narrow.
JP-A-60-192948, JP-A-63-14140, JP-A-63-127237 and JP-A-64-72152 describe photosensitive lithographic printing plates acting as a positive type in which supports are provided with photosensitive layers comprising o-naphthoquinonediazide compounds and coupling components capable of undergoing diazo coupling reaction. However, such photosensitive layers have the disadvantage of being slow in development speed, when processed with weakly alkaline developers, particularly of pH 12.5 or less. According to the aforesaid patent specifications, particularly preferred examples of the coupler residues include naphthols, phloroglucines, pyrazolones, phthalimides, indoxyls, indazolones, acetamides, and .beta.-ketoesters, and of these, pyrazolones are regarded as the most preferred coupler residues. In the aforesaid specifications, however, strongly alkaline developers are used, and processing suitability with weakly alkaline developers, particularly of pH 12.5 or less, is not described. It has been therefore difficult to deduce structures desirable for such weakly alkaline developers.
On the other hand, the prevention of environmental pollution recently requires simplified disposal of industrial waste. It is therefore strongly demanded to lower the pH of processing liquids for positive printing plates.